I got the Fallout 3 collector's edition in physical form when the game was released, and that's all fine and dandy. But is there any way to register it on Steam, as if I had bought it there originally? So I can download it straight from the Steam interface, is what I mean. I tried simply using the Activate A Product On Steam menu option, but it doesn't recognize the key.

Might be it is simply impossible, but if anyone can help, please do.

Not from a physical copy. You have to buy it from Steam to be able to download it from it.

Damn. Thanks anyway.